How do I resolve a timing issue?

I have a 2004 Cadillac SRX 3.6. I installed a used 2007 Saturn Aura long block. The car runs good and has plenty of power. The problem is that it takes a long time to get the engine started and three cam positioning sensor codes won't clear. I had a Cadillac dealership run the diagnostic scans. I was told by the tech that the only way to get the car to perform as it should I would have to replace the camshaft actuators. This will be a realative expensive endeavor and I am just trying to gather enough information to determine if this would be the correct course to proceed upon, or if I should just find a Cadillac replacement engine. If I replace the actuators should I use the Cadillac ones, or the ones which fit the cylinder heads which are installed?
Bob